The inheritance of acquired characteristics is a hypothesis about a mechanism of heredity by which changes in physiology acquired over the life of an organism (such as the enlargement of a muscle through repeated use) may purportedly be transmitted to offspring. It is also commonly referred to as the theory of adaptation equated with the evolutionary theory of FrenchnaturalistJean-Baptiste Lamarck known as Lamarckism. The idea was proposed in ancient times by Hippocrates and Aristotle, and was commonly accepted near to Lamarck's time. Comte de Buffon, before Lamarck, proposed ideas about evolution involving the concept, and even Charles Darwin, after Lamarck, developed his own theory of inheritance of acquired characters, pangenesis. The basic concept of inheritance of acquired characters was finally widely rejected in the early 20th century.

Long after triumph of the central dogma of molecular biology, which is often equated with the idea that the DNA of a cell alone determines its fate, the theory of adaptation continued to attract attention. One of the core ideas that has been used to support the theory of adaptation is the observation that the germ plasm of an egg cell is in part derived from the diploid cells of the parent;[How to reference and link to summary or text] this cytoplasm is hypothesized to influence the early stages of a developing embryo. Since the germ plasm of the egg has a different genotype than that of the egg nucleus itself, supporters of the theory of adaptation looked for examples in which the offspring shared a trait of the parent. Some researchers claimed that in quantitative genetics models that included a maternal effect made more accurate predictions. However, these models have been disproven.

In the 1920s, Harvard University researcher William McDougall studied the abilities of rats to correctly solve mazes. His reports claimed that offspring of rats that had learned the maze were able to run it faster. In his data, the first rats would get it wrong 165 times before being able to run it perfectly each time, but after a few generations, it was down to 20. McDougall attributed this to some sort of Lamarckian evolutionary process. However McDougall's experiments could never be repeated by other experimenters, and have been criticised for having several methodological problems and poor record-keeping.[1][2]